Exploring static routing with IPMininet
In a previous post we have shown that IPMininet can be used to develop exercises that enable students to explore how IPv6 routers forward packets. We used a simple example with only three routers and very simple static routes. In this post, we build a larger network and introduce different static routes on the main routers. Our IPMininet network contains two hosts and five routers.
mininet> nodes
available nodes are:
h1 h2 ra rb rc re
mininet> links
ra-eth2<->h1-eth0 (OK OK)
ra-eth0<->rb-eth0 (OK OK)
ra-eth1<->rc-eth0 (OK OK)
rb-eth1<->rc-eth1 (OK OK)
rb-eth2<->re-eth0 (OK OK)
rc-eth2<->re-eth1 (OK OK)
re-eth2<->h2-eth0 (OK OK)
From this output, it is easy to represent the network as a graph:
+------------+
| |
h1--- ra --- rb --- rc
| |
h2 --- re------+
The two hosts are configured with the following IPv6 addresses and a default route that points to their router.
mininet> h2 ip -6 addr show dev h2-eth0
2: h2-eth0@if4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 2001:2345:2::2/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::4450:34ff:fe19:6c58/64 scope link
valid_lft forever preferred_lft forever
mininet> h1 ip -6 addr show dev h1-eth0
2: h1-eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 2001:2345:1::1/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::5895:51ff:fee2:226b/64 scope link
valid_lft forever preferred_lft forever
mininet> h1 ip -6 route show
2001:2345:1::/64 dev h1-eth0 proto kernel metric 256 pref medium
fe80::/64 dev h1-eth0 proto kernel metric 256 pref medium
default via 2001:2345:1::a dev h1-eth0 metric 1024 pref medium
mininet> h2 ip -6 route show
2001:2345:2::/64 dev h2-eth0 proto kernel metric 256 pref medium
fe80::/64 dev h2-eth0 proto kernel metric 256 pref medium
default via 2001:2345:2::e dev h2-eth0 metric 1024 pref medium
Our first example includes static routes that enable h1 to reach h2 correctly:
mininet> h1 traceroute6 2001:2345:2::2
traceroute to 2001:2345:2::2 (2001:2345:2::2) from 2001:2345:1::1, 30 hops max, 16 byte packets
1 2001:2345:1::a (2001:2345:1::a) 0.479 ms 0.047 ms 0.124 ms
2 2001:2345:4::c (2001:2345:4::c) 0.162 ms 0.166 ms 0.101 ms
3 2001:2345:3::e (2001:2345:3::e) 0.157 ms 0.184 ms 0.198 ms
4 2001:2345:2::2 (2001:2345:2::2) 0.239 ms 0.097 ms 0 ms
mininet> h2 traceroute6 2001:2345:1::1
traceroute to 2001:2345:1::1 (2001:2345:1::1) from 2001:2345:2::2, 30 hops max, 16 byte packets
1 2001:2345:2::e (2001:2345:2::e) 0.067 ms 0.048 ms 0.025 ms
2 2001:2345:3::c (2001:2345:3::c) 0.037 ms 0.036 ms 0.023 ms
3 2001:2345:4::a (2001:2345:4::a) 0.035 ms 0.035 ms 0.025 ms
4 2001:2345:1::1 (2001:2345:1::1) 0.031 ms 0.073 ms 0.025 ms
This can be confirmed by looking at the IPv6 routing tables of routers ra, rc and re
(the loopback addresses have been removed from the output of the ip command ) :
mininet> ra ip -6 addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: ra-eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 2001:2345:1::a/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::5cee:dff:fe3a:bb4b/64 scope link
valid_lft forever preferred_lft forever
3: ra-eth0@ra-eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 2001:2345:7::a/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::acd5:1ff:fe69:9cd/64 scope link
valid_lft forever preferred_lft forever
4: ra-eth1@ra-eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 2001:2345:4::a/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::4497:7aff:fe86:86b7/64 scope link
valid_lft forever preferred_lft forever
mininet> rc ip -6 addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: rc-eth0@rc-eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 2001:2345:4::c/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::ec32:67ff:fe79:435/64 scope link
valid_lft forever preferred_lft forever
3: rc-eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 2001:2345:5::c/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::cca:a9ff:fe17:67e9/64 scope link
valid_lft forever preferred_lft forever
4: rc-eth2@rc-eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 2001:2345:3::c/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::8c3f:e6ff:fe98:f3e5/64 scope link
valid_lft forever preferred_lft forever
mininet> re ip -6 addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: re-eth0@re-eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 2001:2345:6::e/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::c87d:10ff:fe35:5b25/64 scope link
valid_lft forever preferred_lft forever
3: re-eth1@re-eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 2001:2345:3::e/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::cc07:59ff:fe97:3a7d/64 scope link
valid_lft forever preferred_lft forever
4: re-eth2@re-eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 2001:2345:2::e/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::bcfd:cff:fedf:fedb/64 scope link
valid_lft forever preferred_lft forever
mininet> ra ip -6 route show
2001:2345:1::/64 dev ra-eth2 proto kernel metric 256 pref medium
2001:2345:4::/64 dev ra-eth1 proto kernel metric 256 pref medium
2001:2345:7::/64 dev ra-eth0 proto kernel metric 256 pref medium
fe80::/64 dev ra-eth2 proto kernel metric 256 pref medium
fe80::/64 dev ra-eth0 proto kernel metric 256 pref medium
fe80::/64 dev ra-eth1 proto kernel metric 256 pref medium
default via 2001:2345:4::c dev ra-eth1 proto zebra metric 20 pref medium
mininet> rb ip -6 route show
2001:2345:5::/64 dev rb-eth1 proto kernel metric 256 pref medium
2001:2345:6::/64 dev rb-eth2 proto kernel metric 256 pref medium
2001:2345:7::/64 dev rb-eth0 proto kernel metric 256 pref medium
fe80::/64 dev rb-eth0 proto kernel metric 256 pref medium
fe80::/64 dev rb-eth1 proto kernel metric 256 pref medium
fe80::/64 dev rb-eth2 proto kernel metric 256 pref medium
default via 2001:2345:5::c dev rb-eth1 proto zebra metric 20 pref medium
mininet> rc ip -6 route show
2001:2345:1::/48 via 2001:2345:4::a dev rc-eth0 proto zebra metric 20 pref medium
2001:2345:2::/48 via 2001:2345:3::e dev rc-eth2 proto zebra metric 20 pref medium
2001:2345:3::/64 dev rc-eth2 proto kernel metric 256 pref medium
2001:2345:4::/64 dev rc-eth0 proto kernel metric 256 pref medium
2001:2345:5::/64 dev rc-eth1 proto kernel metric 256 pref medium
2001:2345:6::/48 via 2001:2345:5::b dev rc-eth1 proto zebra metric 20 pref medium
2001:2345:7::/48 via 2001:2345:5::b dev rc-eth1 proto zebra metric 20 pref medium
fe80::/64 dev rc-eth0 proto kernel metric 256 pref medium
fe80::/64 dev rc-eth1 proto kernel metric 256 pref medium
fe80::/64 dev rc-eth2 proto kernel metric 256 pref medium
mininet> re ip -6 route show
2001:2345:2::/64 dev re-eth2 proto kernel metric 256 pref medium
2001:2345:3::/64 dev re-eth1 proto kernel metric 256 pref medium
2001:2345:6::/64 dev re-eth0 proto kernel metric 256 pref medium
fe80::/64 dev re-eth0 proto kernel metric 256 pref medium
fe80::/64 dev re-eth1 proto kernel metric 256 pref medium
fe80::/64 dev re-eth2 proto kernel metric 256 pref medium
default via 2001:2345:3::c dev re-eth1 proto zebra metric 20 pref medium
From this information, can you predict the output that traceroute6 will produce between
any pair of routers in the network ? You can check your result by using traceroute6 from
any router or host towards any reachable IPv6 address inside the emulated network. Here is a simple
script to automate those traceroutes.
#!/bin/bash
for dest in 2001:2345:1::1 2001:2345:2::2 2001:2345:1::a 2001:2345:7::a 2001:2345:4::a 2001:2345:7::b 2001:2345:5::b 2001:2345:6::b 2001:2345:4::c 2001:2345:5::c 2001:2345:3::c 2001:2345:6::e 2001:2345:3::e 2001:2345:2::e
do
echo "Running traceroute6 towards ${dest} "
traceroute6 -q 1 ${dest}
done
Another network scenario is provided in static-err.py. This scenario uses the same network topology and IPv6 addresses, but the static routes are different.
mininet> ra ip -6 route show
2001:2345:1::/64 dev ra-eth2 proto kernel metric 256 pref medium
2001:2345:2::/47 via 2001:2345:7::b dev ra-eth0 proto zebra metric 20 pref mdium
2001:2345:4::/64 dev ra-eth1 proto kernel metric 256 pref medium
2001:2345:7::/64 dev ra-eth0 proto kernel metric 256 pref medium
2001:2345:4::/46 via 2001:2345:4::c dev ra-eth1 proto zebra metric 20 pref mdium
fe80::/64 dev ra-eth2 proto kernel metric 256 pref medium
fe80::/64 dev ra-eth0 proto kernel metric 256 pref medium
fe80::/64 dev ra-eth1 proto kernel metric 256 pref medium
mininet> rc ip -6 route show
2001:2345::/47 via 2001:2345:4::a dev rc-eth0 proto zebra metric 20 pref medum
2001:2345:3::/64 dev rc-eth2 proto kernel metric 256 pref medium
2001:2345:2::/47 via 2001:2345:3::e dev rc-eth2 proto zebra metric 20 pref mdium
2001:2345:4::/64 dev rc-eth0 proto kernel metric 256 pref medium
2001:2345:5::/64 dev rc-eth1 proto kernel metric 256 pref medium
2001:2345:6::/47 via 2001:2345:5::b dev rc-eth1 proto zebra metric 20 pref mdium
fe80::/64 dev rc-eth0 proto kernel metric 256 pref medium
fe80::/64 dev rc-eth1 proto kernel metric 256 pref medium
fe80::/64 dev rc-eth2 proto kernel metric 256 pref medium
mininet> re ip -6 route show
2001:2345:2::/64 dev re-eth2 proto kernel metric 256 pref medium
2001:2345:3::/64 dev re-eth1 proto kernel metric 256 pref medium
2001:2345:5::/48 via 2001:2345:3::c dev re-eth1 proto zebra metric 20 pref mdium
2001:2345:6::/64 dev re-eth0 proto kernel metric 256 pref medium
2001:2345::/40 via 2001:2345:6::b dev re-eth0 proto zebra metric 20 pref medum
fe80::/64 dev re-eth0 proto kernel metric 256 pref medium
fe80::/64 dev re-eth1 proto kernel metric 256 pref medium
fe80::/64 dev re-eth2 proto kernel metric 256 pref medium
mininet> rb ip -6 route show
2001:2345:3::/48 via 2001:2345:5::c dev rb-eth1 proto zebra metric 20 pref medium
2001:2345:2::/47 via 2001:2345:6::e dev rb-eth2 proto zebra metric 20 pref medium
2001:2345:5::/64 dev rb-eth1 proto kernel metric 256 pref medium
2001:2345:6::/64 dev rb-eth2 proto kernel metric 256 pref medium
2001:2345:7::/64 dev rb-eth0 proto kernel metric 256 pref medium
2001:2345:4::/46 via 2001:2345:5::c dev rb-eth1 proto zebra metric 20 pref medium
2001:2345::/44 via 2001:2345:7::a dev rb-eth0 proto zebra metric 20 pref medium
fe80::/64 dev rb-eth0 proto kernel metric 256 pref medium
fe80::/64 dev rb-eth1 proto kernel metric 256 pref medium
fe80::/64 dev rb-eth2 proto kernel metric 256 pref medium
In these routing tables, note the length of the different prefixes. When analysing how packets are forwarded by each router, remember that they use the most specific match in the routing table.
Written on November 28, 2017